Magnon satellite bands in the optical spectrum of antiferromagnetic Rb<Subscript>2</Subscript>MnCl<Subscript>4</Subscript>

The evolution of optical absorption in a two-dimensional antiferromagnet is investigated in the range of the transition ⁶A_1g → ⁴A_1g, ⁴E _g (⁴G) observed in manganese ions in an external magnetic field inducing noncollinearity of the magnetic structure. It is revealed that hot and cold satellites of the exciton-magnon bands appear in the optical absorption spectrum and then increase in intensity. The shapes of the magnon satellite bands corresponding to a two-dimensional magnetic structure are calculated. It is demonstrated that magnons at the inner points of the Brillouin zone appreciably contribute to the absorption. The zero-point magnetic oscillations play a decisive role in the absorption associated with the magnon decay at low temperatures.     

Optical Investigation of the Phase State of a Dilute Antiferromagnet

The behavior of exciton-magnon light absorption bands of Rb₂Mn _x Cd_1–x Cl₄ crystals in the region of the ⁶ A _1g ⁴ T _2g (⁴ D) optical transition of manganese ions in a magnetic field is used to construct magnetic phase state diagrams. The x-H and x-T diagrams are constructed. The components of the g-factor are determined for the examined excited state.     

Spectral studies of Nd3+ and Er3+ ions in POCl3:SnCl4 laser liquid

The optical absorption spectra of triply ionized neodymium and erbium ions in POCl₃SnCl₄ laser liquid have been studied for the first time in the UV-VIS and NIR regions. Spectroscopic and Judd-Ofelt intensity parameters are evaluated from the observed band positions and their intensities. Radiative lifetimes and the luminescent branching ratios for the excited fluorescent levels of Nd³⁺ and Er³⁺ ions are theoretically estimated and the possible laser transitions are indicated. From the observed splittings of certain bands in the second-derivative spectrum of the Nd³⁺ ion, the crystal field (A ₂₀,A ₄₀) parameters are evaluated assumingC _3h symmetry for the ion.     

Electron paramagnetic resonance and optical absorption studies of manganese ions doped in polyvinyl(alcohol) complexed with polyethylene glycol polymer films

Electron paramagnetic resonance (EPR), optical absorption, and infrared spectral studies have been carried out on Mn²⁺ ions doped in poly(vinyl alcohol) (PVA) complexed with polyethylene glycol (PEG) films prepared by solution cast technique. The EPR spectra of 0.25?mol% Mn²⁺ ions doped polymer complex (PVA+PEG) at room temperature exhibit sextet hyperfine structure (hfs), centered at g????1.99. The spin?CHamiltonian parameter values indicate that the ground state of Mn²⁺ ion is d⁵ and the site symmetry around Mn²⁺ ions in tetragonally distorted octahedral site. The spin concentration participating in the resonance is measured as a function of temperature and it is observed that it obeys Boltzmann??s law. The paramagnetic susceptibility (??) is calculated from the EPR data at various temperatures (93?C333?K) and it obeys the Curie?CWeiss law. The optical absorption spectra exhibits two bands which are assigned to ⁶A_1g (S)??⁴A_1g (G) or ⁴E_g (G) and ⁶A_1g (S)??⁴T_2g (G) transitions. The infrared spectrum exhibits few bands due to the presence of O?CH, C?CH, and C=C groups.     

Visible and near-infrared absorption of LiCl crystal with divalent nickel

Absorption spectra of thed-d transition in the LiCl: Ni²⁺ crystals were measured. It was deduced therefrom that the absorption bands belong to the octahedrally coordinated divalent nickel like in the other alkali chloride crystals of NaCl type. The observed structure connected with³A_2g ³T _1g ^/a ,¹ E _g transitions has been discussed.Cukrovarnická 10, Praha 6, Czechoslovakia.We are grateful to J. Trnka for polarographic measurements of the concentration of Ni²⁺ in samples measured and to A. Bohun for discussions.     

Linear and nonlinear optical spectroscopy of gadolinium iron borate GdFe<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript>

The optical spectra and the second-harmonic generation (SHG) are studied in a noncentrosymmetric GdFe₃(BO₃)₄ magnet. In the region of weak absorption (α～20–400 cm^?1) below ～3 eV, three absorption bands are distinguished, which can be unambiguously assigned to forbidden electronic transitions from the ground ⁶A₁ state of the Fe³⁺ ion to its excited states ⁴T₁(～1.4 eV), ⁴T₂(～2 eV), and ⁴A₁, ⁴E(～2.8 eV). Intense absorption begins in the region above 3 eV (α～2–4×10⁵ cm^?1), where two bands at ～4.0 and 4.8 eV are observed, which are caused by allowed electric dipole charge-transfer transitions. The spectral features of SHG in the 1.2–3.0-eV region are explained by a change in the SHG efficiency caused by a change in the phase mismatch. It is shown that in the weak absorption region, phase matching can be achieved for SHG.     

Mixed alkali effect in borate glasses—EPR and optical absorption studies in xNa2O–(30−x)K2O–70B2O3 glasses doped with Mn2+

The mixed alkali borate xNa₂O–(30−x)K₂O–70B₂O₃ (5≤x≤25) glasses doped with 1 mol% of manganese ions were investigated using EPR and optical absorption techniques as a function of alkali content to look for ‘mixed alkali effect’ (MAE) on the spectral properties of the glasses. The EPR spectra of all the investigated samples exhibit resonance signals which are characteristic of the Mn²⁺ ions. The resonance signal at g≅2.02 exhibits a six line hyperfine structure. In addition to this, a prominent peak with g≅4.64, with a shoulder around g≅4.05 and 2.98, was also observed. From the observed EPR spectrum, the spin-Hamiltonian parameters g and A have been evaluated. It is interesting to note that some of the EPR parameters do show MAE. It is found that the ionic character increases with x and reaches a maximum around x=20 and thereafter it decreases showing the MAE. The number of spins participating in resonance (N) at g≅2.02 decreases with x and reaches a minimum around x=20 and thereafter it increases showing the MAE. It is also observed that the zero-field splitting parameter (D) increases with x, reaches a maximum around x=15 and thereafter decreases showing the MAE. The optical absorption spectrum exhibits a broad band around ∼20,000 cm⁻¹ which has been assigned to the transition ⁶A_1g(S)→⁴T_1g(G). From ultraviolet absorption edges, the optical bandgap energies and Urbach energies were evaluated. It is interesting to note that the Urbach energies for these glasses decrease with x and reach a minimum around x=15. The optical band gaps obtained in the present work lie in the range 3.28–3.40 eV for both the direct and indirect transitions. The physical parameters of all the glasses were also evaluated with respect to the composition.     

Absorption of light by exchange-coupled ions in a 2D antiferromagnet

The optical absorption spectra of Rb₂Mn_xCd_1?xCl₄ crystals are experimentally studied in the vicinity of a magnon sideband of the exciton band at a manganese content x ranging from 1.0 to 0.4. Additional absorption bands are observed with an increase in the magnetic structural disorder upon replacement of manganese ions by cadmium ions. An analysis of the evolution of the additional absorption bands in a magnetic field during the spin-flop phase transition and the change in the intensity with variations in the manganese content x demonstrates that these bands are associated with the excitation of the exchange-coupled pairs of manganese ions located in different environments in a plane square lattice. The phase boundary between the antiferromagnetic and spin-flop phases is constructed using the results of optical measurements. The manganese content corresponding to the magnetic percolation point is evaluated.     

Spectral studies on Cr ions doped in sodium-lead borophosphate glasses

Electron paramagnetic resonance (EPR), optical absorption and emission spectra of Cr³⁺ ions doped in (30−x) (NaPO₃)₆+30PbO+40B₂O₃+xCr₂O₃ (x=0.5, 2.0, 3.0, 4.0 and 5.0 mol%) glasses have been studied. The EPR spectra exhibit resonance signals with effective g values at g≈4.55 and g≈1.97. The EPR spectra of x=3.0 mol% of Cr₂O₃ in sodium-lead borophosphate glass sample were studied at various temperatures (295-123 K). The intensity of the resonance signals increases with decrease in temperature. The optical absorption spectrum exhibits four bands characteristic of Cr³⁺ ions in octahedral symmetry. From the analysis of the bands, the crystal-field parameter Dq and the Racah interelectronic repulsion parameters B and C have been evaluated. The emission spectrum exhibit one broad band characteristic of Cr³⁺ ions in octahedral symmetry. This band has been assigned to the transition ⁴T_2g (F)→⁴A_2g (F). Correlating EPR and optical data, the molecular bonding coefficient (α) has been evaluated.     

On the role of theΔ -isobar in deep inelastic scattering on the deuteron

The role of the nuclear structure effects, viz. the boundness of nucleons and-isobar components, in the deep inelastic scattering of leptons on the deuteron is considered. It is shown that small admixture of the-isobar configurations to the deuteron wave function may lead to significant effects in the spin structure functions of the deuteronb ₁ ^D andg ₁ ^D (x): up to 4% in g ₁ ^D (x) dx and up to 10% ing ₁ ^D (x) at smallx.One of the authors (A.U.) thanks Prof. F.C. Khanna for helpful discussions and for kind offering the information used in our calculations.     

Optical properties of CdIn2Se4 thin films

The optical constants (the refractive index n, the absorption index k, and the absorption coefficient ) of CdIn₂Se₄ thin films were determined in the spectral range of 500–2000 nm. Graphical representation of log() as a function of log(1/) shows two distinct, linear parts indicating the existance of both direct and indirect optical transitions. The corresponding forbidden energy gaps E _g ^d and E _g ^Emphasis>d were determined. The effect of both annealing temperature as well as the substrate temperature on the optical constants of CdIn₂Se₄ thin films was also investigated.     

Absorption Spectra and Thermostimulated Luminescence of Irradiated KBr Crystals with a High Content of an Na Impurity

The influence of high concentrations of the Na⁺ impurity on the photo and thermostimulated luminescence in an xirradiated KBr crystal has been studied. It is revealed that at an impurity concentration of 1 mol.% the absorption spectrum of the KBr:Na crystal possesses only the bands belonging to the (, I _A) and (F, H _A) pairs of the centers and that the thermoluminescence spectrum consists of two peaks with a maximum at 140 and 165 K.     

Deutung der optischen Absorptionsspektren der Übergangselemente der Eisenreihe,insbesondere der des Rubins

Crystal field, ligand field and molecular orbital theories have been used to explain the optical spectra of transition elements. It is shown an additional possibility to explain the absorption bands of the transition elements, especially those of ruby, as transitions not between the nonbondingt _2g and the antibondinge _g ^* but between the bondinga _1g and the nonbondingt _2g.     

Spectroscopic properties of alexandrite crystals II

Several aspects of the optical spectroscopic properties of alexandrite crystals not previously investigated are reported here. For Cr³⁺ ions occupying the Al³⁺ lattice sites with mirror symmetry in BeAl₂O₄, the positions of the zero-phonon lines for absorption transitions to the ²T_1g and ⁴T_2g levels are identified, and vibronic transition peaks in the fluorescence spectrum are compared to transitions appearing in the Raman spectrum and Stokes excitation spectrum. In addition, the effects of radiation trapping are shown to lengthen the fluorescence lifetime of the ²E_g - ⁴A_2g transition for ions in these sites at low temperatures. For Cr³⁺ ions occupying the Al³⁺ lattice with inversion symmetry, the ground state splitting of the ²E_g - ⁴A_2g transition is reported and the decrease of the fluorescence lifetime with temperature is shown to be due to the increase in vibronic emission probability as well as increased probability of direct radiationless decay.     

The magnetic circular dichroism spectrum of the 1 B 2u ←1 A 1g transition of benzene in the vapour phase

The magnetic circular dichroism (MCD) spectrum of the ¹ B _2u ←¹ A _1g transition of benzene has been measured in the vapour phase. Many of the bands due to transitions between single vibronic levels display A terms. It has been shown that the angular momentum arises by vibronic mixing both of the ¹ E _1u state with the ¹ B _1u state and of the ¹ E _2g states with the ¹ A _1g ground state by e _2g vibrations. The magnitudes and signs of the experimental and calculated ratios, A/D, for the A ₀ ⁰ vibronic origin are in excellent agreement. Two strong MCD progressions of opposite sign with B-term dispersion have been observed in regions of low absorption. These are identified with vibronic origins due to the v ₈ and v ₉ e _2g modes. By contrast the MCD spectrum of hexadeuterobenzene vapour has a much lower magneto-rotational strength and displays none of the striking features of the benzene MCD spectrum.     

Oscillations of the photon echo intensity in a pulsed magnetic field: Zeeman splitting in LiLuF<Subscript>4</Subscript>:Er<Superscript>3+</Superscript>

A method of high-resolution time-resolved optical spectroscopy using oscillations of the photon echo intensity in the presence of a perturbation, which splits the optical frequencies of the transitions of two or more ion subgroups, has been proposed and demonstrated. This method has been applied to systems in which the Zee-man effect is manifested. The transition frequencies of ions are switched by a pulsed magnetic field. Oscillations of the photon echo intensity were observed in LiLuF₄:Er³⁺ and LiYF₄:Er³⁺. The first minimum corresponding to the accumulated phase of the electric dipole moment π/2 is reached in the pulsed magnetic field with an amplitude of ～2 G at a duration of 30 ns. The Zeeman splitting in this field is ～10 MHz, which is much less than the laser spectral width (0.15 Å ～ 9 GHz). The g factor of the ⁴ F _9/2(I) excited state of the Er³⁺ ion in the LiLuF₄ matrix has been determined in zero magnetic field. The comparison with the g-factor value found from the measurement of the absorption spectrum in a magnetic field of 8 kG has been performed.     

Growth, EPR and optical absorption spectra of l-threonine single crystals doped with Cu ions

We investigated the crystal growth, electron paramagnetic resonance (EPR) and optical absorption spectra of l-threonine doped with Cu²⁺. The quality, size and habit of the single crystals grown from aqueous solution by the slow solvent evaporation and by the cooling methods vary when the impurities are introduced during the growth process. The variations with the magnetic field orientation of the EPR spectra of single-crystal samples at room temperature and 9.77 GHz in three crystal planes (ab, bc and ac) show the presence of copper impurities in four symmetry-related sites of the unit cell. These spectra display well resolved hyperfine couplings of the of Cu²⁺ with the I_Cu= of the copper nuclei. Additional hyperfine splittings, well-resolved only for specific orientations of the magnetic field, indicate that the copper impurity ions in the interstitial sites have two N ligands with similar hyperfine couplings. The principal values of the g and A_Cu tensors calculated from the EPR data are g₁=2.051(1), g₂=2.062(2), g₃=2.260(2), A_Cu,1=16.9(5)×10⁻⁴ cm⁻¹, A_Cu,2=21.8(6)×10⁻⁴ cm⁻¹, A_Cu,3=180.0(5)×10⁻⁴ cm⁻¹. The principal directions corresponding to g₃ and to A_Cu,3 are coincident within the experimental errors, reflecting the orientation of the bonding planes of the copper ions in the crystal. The values of the crystal field energies are evaluated from the optical absorption spectrum, and the crystal field and bonding parameters of the Cu impurities in the crystal are calculated and analyzed. The EPR and optical absorption results are discussed in terms of the crystal structure of l-threonine and the electronic structure of the Cu²⁺ ions, and compared with data reported for other systems. The effects of the impurities in the growth and habit of the crystals are also discussed.     

Optical absorption in cubic Zn1-xMnxSe under hydrostatic pressure

The optical absorption edges of the diluted magnetic semiconductors Zn_1-xMn_xSe have been measured under hydrostatic pressure for x ≦ 0.25. We found a blue shift of the direct interband gap with pressure which is nearly independent of the manganese concentration. An absorption band at 2.62 eV is assigned to the intra-atomic transition ⁶A₁ → ⁴A₁, ⁴E of the manganese ions. Its pressure shift indicates an increase of the d-p-hybridization which is, however, weaker than in the tellurides. Additional bands appear at sufficiently high pressures in samples with x = 0.15 and 0.25.